AWS Certified Solutions Architect - Professional 2020

Sign Up Free or Log In to participate!

Doubt about exam simulator question around public ledger/QLDB

Hi  CloudGuru experts,

I came across following question in exam simulator that givesQLDB as an answer. From AWS documentation "If your application requires decentralization and involves multiple, untrusted parties, a blockchain solution may be appropriate. If your application requires a complete and verifiable history of all application data changes, but does not involve multiple, untrusted parties, Amazon QLDB is a great fit.". Case described in question involves multiple independent actors such as producers & end retailers. Correct answer should be Blockchain. Please comment and correct me if needed, 


You work for an organic produce importer and the company is trying to find ways to better engage with its supply chain. One idea is to create a public ledger that all members of the supply chain could update and query as products changed hands along the journey to the customer. Then, your company could create an app that would allow consumers to view the chain from producer to end retailer and have confidence in the product sourcing. Which AWS service or services could most directly help realize this vision?

1. Amazon P2PShare and API Gateway
2. Amazon QLDB
3. Amazon DynamoDB and Lambda
4. Amazon Managed Blockchain
5. Amazon CloudTrail and API Gateway


Amazon Quantum Ledger Database (QLDB) is a fully-managed ledger database that provides a transparent, immutable and verifiable transaction log. While other products could be used to create such a supply chain logging solution, QLDB is the closest to a ready-made solution.

1 Answers

If nothing else the key is that the Produce Importer is creating a ledger that they own. Hence, "QLDB is a ledger database purpose-built for customers who need to maintain a complete and verifiable history of data changes in an application that they own."

QLDB – Retail & Supply Chain

Retailers often need to access information on every stage of a product’s supply chain, such as what location did the product come from, how many items of the product were shipped and to whom, who handled the shipment, etc. With QLDB, retail companies can look back and track the full history of inventory and supply chain transactions at every logistical stage of their products.

So I feel it is pretty clear with that last line that QLDB would be the answer here.

Managed Blockchain – 

Supply Chain

Small businesses often rely on distributed supply chain networks where no single entity controls the end-to-end movement of goods across the network. As an example, jewelry stores often need to track the provenance of gemstones to ensure their authenticity and value. Using Amazon Managed Blockchain, such businesses can quickly implement a blockchain across their supply chain network, providing greater transparency, and real-time recording and tracking of goods from one party to another. Each supplier or distributor can be a member of the blockchain network, maintain their own distributed ledger, and independently track all information related to the movement of the goods such as timestamp, port of entry, and volume of goods received. Given that all members maintain an independent copy of the distributed ledger, all parties can trust the true origin and touchpoints of the goods, without relying on a central authority.


With an extensive background in supply chain, and a fairly deep experience in blockchain and distributed ledgers, I politely disagree. Participants of a supply chain are spread across countries, and are independent companies. Your typical supply chain may involve a manufacturer in China, local shipper in china, a global sea or air shipper, then local logistics services in your area, and then your intermediaries and other retailers. these actors are independent and untrusted. Stated problem is a very well known supply chain use case. While one actor may own the public database, all of these actors must be able to add to it. QLDB is for internal trusted participants. QLDB is not the answer.

Josh Griswell

It’s not going to be on the real exam regardless. But, all I can say is that I disagree. Based on the key wording in the question and the product description I still would go with QLDB.

Antti Haapakoski

There are private ledgers, consortium ledgers and public ledgers in the ledger technology. A "public ledger" refers to a public blockchain like Ethereum.

Antti Haapakoski

So I would say QLDB is not the right answer: it is a private or consortium ledger. Only public ledger offered by AWS is Ethereum in Amazon Managed Blockchain.

Antti Haapakoski

Sign In
Welcome Back!

Psst…this one if you’ve been moved to ACG!

Get Started
Who’s going to be learning?